1. Field of the Invention
The invention relates to an ink feeder for supplying ink from a main ink tank to an ink subtank via an ink supply port, and supplying ink from the ink subtank to a print head via an ink outlet in an ink-jet printer or other device.
2. Description of the Related Art
A conventional ink feeder for supplying ink from a main ink tank to an ink subtank via an ink supply port, and supplying ink from the ink subtank to a print head via an ink outlet, is disclosed in Japanese Published Examined Patent Application No. Sho 63-44064.
As shown in FIGS. 9 and 10, the ink subtank of a conventional ink feeder is provided to supply ink, that is supplied from a main tank 208 via a tube 209 and an ink inlet 206A of a capillary tube 206, to a print head via an ink outlet 207A of a capillary tube 207 under a predetermined pressure. The interior of a casing 201 of the ink subtank stores ink, and is partitioned into multiple ink chambers A1 and A2 by a partition wall 203. The partition wall 203 has an upper communicating part 204 which allows the movement of air in its upper part, and a lower communicating hole 205 provided with resistant action which allows the movement of ink in its lower part. In the ink feeder disclosed in the above patent application, the ink subtank is filled with a large quantity of ink due to the partition wall 203 and the resistant action of the lower communicating hole 205. As shown in FIG. 10, the ink inlet 206A, the lower communicating hole 205 and the ink output 207A are approximately aligned.
In this type of ink feeder, to maintain printing quality, air, that is, a bubble in the ink, is separated in the ink subtank to prevent the bubble from flowing on the side of the print head, and the pressure of ink which acts upon the print head is set to a predetermined value based upon the positional relationship between the level of ink in the ink subtank and the print head.
However, a bubble may not be separated from the ink and may enter the print head, depending upon the position and the size of the lower communicating hole of the partition wall. However, the ink feeder that is provided with the lower communicating hole provided with resistant action and disclosed in the above patent application is subject to various problems. Specifically, it takes too long to fill the ink subtank with ink, the start of printing is delayed until the level of each ink chamber is equal, the level of each ink chamber becomes uneven, the supplement of ink is delayed and the pressure of ink which acts upon the print head is off a set value as ink is consumed, and printing quality is often deteriorated.
As shown in FIG. 8, for example, an ink subtank 101 previously devised by the inventors of the present invention is provided with a casing 102 that has an upper opening for storing ink and a cover 103 for closing the upper opening of the casing 102. The interior of the casing 102 is partitioned into first to third ink chambers 110, 111 and 112 by partition walls 108 and 109, that are respectively provided with upper communicating parts 104 and 105 which allow the movement of air in its upper part, and lower communicating holes 106 and 107 which allow the movement of ink in its lower part. Air is separated from the ink by making ink, that is supplied from an ink supply port 101A, meander in each ink chamber 110 to 112 in the ink subtank 101, so that only ink is moved to the print head via an ink outlet 101B.
An ink sensor 113, for detecting the quantity of ink, is provided at the first ink chamber 110. An air communicating hole 114, which exposes the third ink chamber to the air, is provided at a portion of the cover 103 that is opposite to the third ink chamber 112. When the ink sensor 113 detects that ink in the ink subtank 101 is decreasing as ink is jetted from the print head, a delivery device, such as a pump, is driven and ink is supplied from a main ink tank (not shown).
Since, in this type of ink subtank, ink supplied from the main ink tank is supplied to the print head under predetermined pressure, the positional relationship between the level of ink in the ink subtank and the print head effects the pressure in the print head and printing quality.
In the ink subtank 101 that has multiple ink chambers 110 to 112, when the ink subtank is carried, or an impact is applied to it, the level of ink in each ink chamber fluctuates. Ink may thus pass the upper communicating parts 104 and 105, and an ink film may be formed in the upper communicating parts 104 and 105 by the surface tension of ink when the ink passes. When the ink film is formed in the upper communicating parts 104 and 105 as described above, the ink chambers 110 and 111 each become a closed space. Since the level in the ink chamber 110 is unchanged independent of the state of ink in another ink chamber, if the ink chamber 110 that is provided with the ink sensor 113 becomes a closed space, for example, the ink sensor 113 is kept in either an on or off state.
If the ink sensor 113 is off, it is judged that there is not much ink, the pump is driven, and ink is supplied to the first ink chamber 110 via the ink supply port 101A. However, since the ink chamber 110 is a closed space and the level of ink is hardly changed, the supply of ink from the main ink tank is continued. As a result, ink flows into the second and third ink chambers 111 and 112, respectively, via the lower communicating holes 106 and 107, ink is excessively supplied, each level of the second and third ink chambers 111 and 112 rises, and ink may overflow to the exterior via the air communicating hole 114.
In the meantime, if the ink sensor 113 is on, it is judged that ink remains in the ink chamber, and ink is not supplied to the first ink chamber 110. However, since the first ink chamber 110 is a closed space, the level of ink is hardly changed even if ink is consumed because of the supply of ink to the print head and ink continues to not be supplied. As a result, ink is not supplied, only ink in the second and third ink chambers 111 and 112 continues to be consumed. Finally, the amount of ink in both ink chambers 111 and 112 becomes low, and it may occur that ink cannot be supplied to the print head and the amount of ink may become low. Even if no extreme state occurs, the level of each ink chamber cannot be controlled, pressure in the print head is changed and such a state has an effect upon printing quality.